Work machines are commonly used to move heavy loads, such as, for example, earth, construction material, and/or debris. These work machines, which may be, for example, wheel loaders, excavators, front shovels, motor graders, bulldozers, backhoes, and track loaders, typically include at least two types of power systems, a propulsion system and a work implement system. The propulsion system may be used, for example, to move the work machine around or between work sites and the work implement system may be used, for example, to move a work implement through a work cycle at a job site.
These work machines typically include a hydraulic system that provides power to both the propulsion system and the work implement system. These types of hydraulic systems typically include a series of hydraulic actuators that operate the propulsion system and the work implement system. For example, one or more hydraulic cylinders and/or hydraulic motors may be used to operate the work implement system and one or more hydraulic motors may be used to operate the propulsion system.
A hydraulic actuator in a hydraulic system may be damaged if the hydraulic actuator experiences cavitation. A hydraulic motor, for example, may experience cavitation when the supply fluid flow to the hydraulic motor is less than the return fluid flow from the motor. This situation may occur when the flow of supply fluid to the hydraulic motor is stopped to thereby stop the motion of the hydraulic motor. The inertia within the hydraulic motor may tend to keep the hydraulic motor rotating. In the absence of a supply of make-up fluid flow to the inlet side of the hydraulic motor, the hydraulic motor may experience cavitation. Any such occurrence of cavitation may result in damage to the hydraulic system and, in particular, to the hydraulic actuator that experiences the cavitation. In addition, an occurrence of cavitation may result in the generation of an unpleasant noise.
As shown in U.S. Pat. No. 5,673,605, one approach for reducing cavitation in a hydraulic motor involves placing a back-pressure valve in a fluid return line from the hydraulic motor. The back-pressure valve maintains a certain magnitude of fluid pressure in the fluid return line between the back-pressure valve and the hydraulic motor. This pressurized fluid acts to oppose the motion of the hydraulic motor. Thus, when the supply of fluid to the motor is stopped, the pressure of the fluid in the return line may act to prevent continued motion of the motor and thereby prevent cavitation on the supply side of the hydraulic motor.
However, maintaining a back pressure in the fluid return line may act to reduce the efficiency of the hydraulic motor. The power generated by a hydraulic motor is a function of the pressure differential over the hydraulic motor. Increasing the back pressure against the hydraulic motor will therefore act to reduce the power generated by the hydraulic motor. The reduction in power translates to a reduction in efficiency that may be particularly apparent in situations where the hydraulic motor is operated for a substantial period of time, such as, for example, when the work machine is traveling over a significant distance.
The hydraulic system of the present disclosure solves one or more of the problems set forth above.